Thanks for encouraging all your kids to write! There’s no way to use one parent email address to sign up multiple children. But, you can use this workaround:
1) Sign up for an educator account (as yourself).
2) Start a classroom.
3) Give your classroom code to your kids. When they sign up as young writers, they should select "Join a class" option in Step 3, then input that classroom code to join your class.
4) When they're finishing the sign up process, they DO NOT need to input an email address at all (because they're signing up with your class, vs. on their own). There will still be a box for email, but it's optional.
You can find more tips on how to do all those things here: